Abnormalities of the first metatarsophalangeal joint encompass a variety of disorders, including hallux abductovalgus (commonly known as “bunions”), hallux varus, hallux limitus, hallux rigidus, and other disorders.
Hallux abductovalgus (“hallux abductovalgus”) is one of the most frequently seen abnormalities of the first metatarsophalangeal joint. In a patient with hallux abductovalgus, the proximal phalanx of the hallux (the great toe) points toward the second toe. This results in a lateral deviation of the great toe (tilting of the great toe away from the mid-line of the body) and a widening of the angle between the first and second metatarsals.
One of the greatest deforming forces in the development of hallux abductovalgus is the adductor hallucis muscle. This muscle has two muscle bellies, a transverse and an oblique. In a patient with hallux abductovalgus, the adductor hallucis muscle gains mechanical advantage, pulling the hallux laterally and forcing the metatarsal head medially.
The severity of hallux abductovalgus deformities has traditionally been quantified based on a variety of measurements from radiographs. One common measurement is the intermetatarsal angle between the line of the first and second metatarsal. Normally, this angle can average from about 6 to about 8 degrees. In a patient with hallux abductovalgus, the intermetatarsal angle is increased, with severe abnormalities measuring greater than 30 degrees. Another common measurement is the hallux abductus angle, which is the angle between the longitudinal axes of the first metatarsal and the great toe. Normally, this angle can average from about 10 to about 15 degrees. In hallux abductovalgus, the hallux abductus angle is increased, with extreme cases measuring greater than 70 degrees. A third common measurement is the tibial sesamoid position. With hallux abductovalgus, the first metatarsal deviates medially off of the sesamoids, causing apparent lateral dislocation. The position of the tibial sesamoid in relation to a line drawn through the mid-longitudinal axis of the first metatarsal determines the tibial sesamoid position.
Hallux varus is an abnormality of the first metatarsophalangeal joint in which the proximal phalanx of the hallux (great toe) points away from the second toe. This results in a medial deviation of the great toe (tilting of the great toe toward the mid-line of the body). A common deforming force in the development of hallux varus is the abductor hallucis muscle. In a patient with hallux varus, the abductor hallucis muscle can gain mechanical advantage, pulling the hallux medially and forcing the metatarsal head laterally.
Hallux limitus is an abnormality of the first metatarsophalangeal joint that results in a restricted range of motion in the first metatarsophalangeal joint. Normally, the range of motion in the first metatarsophalangeal joint can average from about 55 to about 75 degrees. In a patient with hallux limitus, this range of motion is decreased. When the range of motion becomes less than about 5 degrees, this condition is commonly referred to as hallux rigidus (stiff great toe).
Hallux limitus can be functional or structural. Functional hallux limitus exhibits a restricted range of motion in the first metatarsophalangeal joint only during weightbearing. Structural hallux limitus, on the other hand, exhibits a restricted range of motion in the first metatarsophalangeal joint both during weightbearing and non-weightbearing.